The present invention relates to digital video signal processing, and more particularly to architectures and methods for digital camera front-ends.
Imaging and video capabilities have become the trend in consumer electronics. Digital cameras, digital camcorders, and video cellular phones are common, and many other new gadgets are evolving in the market. Advances in large resolution CCD/CMOS sensors coupled with the availability of low-power digital signal processors (DSPs) has led to the development of digital cameras with both high resolution image and short audio/visual clip capabilities. The high resolution (e.g., a 5 megapixel sensor with a 2560×1920 pixel array) provides quality offered by traditional film cameras.
FIG. 2a is a typical functional block diagram for digital camera control and image processing (the “image pipeline”). The automatic focus, automatic exposure, and automatic white balancing are referred to as the 3A functions; and the image processing includes functions such as color filter array (CFA) interpolation, gamma correction, white balancing, color space conversion, and JPEG/MPEG compression/decompression (JPEG for single images and MPEG for video clips). Note that the typical color CCD consists of a rectangular array of photosites (pixels) with each photosite covered by a filter (the CFA): typically, red, green, or blue. In the commonly-used Bayer pattern CFA one-half of the photosites are green, one-quarter are red, and one-quarter are blue.
Typical digital cameras provide a capture mode with full resolution image or audio/visual clip processing plus compression and storage, a preview mode with lower resolution processing for immediate display, and a playback mode for displaying stored images or audio/visual clips.
When a digital image is captured indoors and the subject is at a distance from the camera, any use of zoom without a tri-pod will cause the image to be blurred due to operator jitter during the increased integration time for sensor acquisition to accommodate the low-light conditions. In general, low-light conditions require long exposure times (time for charge integration in a CCD or CMOS sensor) to yield an acceptable signal-to-noise ratio; and with electronic zoom, only a portion of the sensor is used, so the integration time is further multiplied.